1. Field of the Invention
The present invention relates to a common mode filter which is mainly used for a small-sized electronic appliance, and more particularly to a common mode filter which can effectively deal with noises in a power source line which is small in size but requires a relatively large current or data line in a low-profiled appliance such as a digital vide camera, MD (mini disk) player, CD (compact disk) player, portable PC (personal computer), etc.
2. Discussion of the Background
There is proposed a conventional inductor with a winding wound around a drum-shaped core disclosed in JP-A-8-213248, in which as shown in FIG. 5A, electrodes 32 of a film-like conductor formed by plating are attached to flanges at both ends of the drum-shaped core 30 with a winding 33, terminals 33a of the winding 22 are connected to the electrodes 32 by press-welding, and a film 35 is fixed on the upper surface of the core 30 by an adhesive 34.
FIGS. 5B and 5C shows a chip inductor disclosed in JP-A-8-186028 in which a plate-like core 38 is combined with a drum-shaped core with flanges 36 at both ends and terminals 39a of a winding 39 are fixed to electrodes 40 attached to the flange 36 by soldering or like.
In the structure shown in FIGS. 5A or FIGS. 5B and 5C, in which the winding terminals 33a and 39a are crushed flat, a DC resistance may be increased and the terminals may be broken. Therefore, such a structure is difficult to realize the inductor with a relatively small size for a large current in which the product generates a large quantity of heat. The electrode shape shown in FIGS. 5B and 5C, in which the winding terminal 39a fixed on the bottom of the flange 36 is soldered to a printed board, is difficult to recognize the connection state after board mounting. Similarly, since the shape of the electrode 32 shown in FIG. 5A has a short end surface, it is also difficult to recognize the soldering state.
In view of the above, the present invention intends to provide a common mode filter which is small in size but can be used for a relatively large current, can be easily recognized in its mounted state on a substrate and can be low-profiled.
The common mode filter according to the present invention includes a drum-shaped core having flanges at both ends of a winding core around which a winding is wound and a plate-like core with both ends fixed to the flanges to form a closed path between itself and the drum-shaped core, in that concave portions are formed in at least one of facing potions of both cores to provide gaps between the flanges of the drum-shaped core and the plate-like core; and a plurality of electrodes each of which is successive over a upper surface, end surface and lower surface of each flange are provided at portions corresponding to the gaps in each of the flanges; and a plurality of windings are wound around the winding core, both ends of each of the plurality of windings being connected and secured to the electrodes on the upper surface of each of the flanges, respectively; and the drum-shaped core and the plate-like core are fixed to each other by an adhesive.
In this way, the winding terminal is fixed to the electrode in such a manner that it is housed in a gap formed by the concave portion between the flange and plate-like core. Therefore, the winding terminal can be housed in the form of a round wiring. This contributes to providing a common mode filter which is small in size and can be used for a relatively large current. The winding terminal will not be broken since it is not required to be flattened. Further, since the winding terminal is housed in the gap formed by the concave portion, the height of the upper surface of the plate-like core can be suppressed, thus providing a low-profiled common mode filter for a relatively large current. The electrode is provided so as to be successive over the upper surface, end surface and lower surface of the flange. Therefore, when the common mode filter is mounted on the printed board by soldering, on the end surface of the flange, the electrode portion on the upper surface of the flange to which the winding terminal is connected is discriminated from the electrode portion on the end surface and the lower surface of the flange which is to be used for mounting on the printed board, and the electrode portion on the upper surface which may be deteriorated when the winding terminal is connected is not used for mounting. For this reason, the adverse effect on the capability of soldering can be prevented. Furthermore, the fixing state of the solder on the electrodes can be visually recognized.
In the common mode filter, the gaps may be filled with the adhesive.
Since the gaps formed by the concave portions are filled with the adhesive, the winding terminals are reinforced and the quantity of the adhesive is assured so that the plate-like core can be firmly secured to the drum-shaped core.